Is there a Blender icon reference for the Outliner editor?
Use the Icon Viewer add-on and outliner_draw.c file.

Enable the Icon Viewer add-on.
In Icon Viewer, click on the icon you're trying to lookup. 
In an Info editor, note the name of the icon. This may be descriptive enough on it's own, but if not, proceed to the next step. In this example, it is GHOST_ENABLED. 
Go to outliner_draw.c and look for the same text, GHOST_ENABLED in this example. You should find the type of object the icon represents in the case statement right above the icon name. In this example, you can see it is a proxy. 

Using the same process for the broken paper icon shows it is LIBRARY_DATA_BROKEN.